The present invention relates to a composite plastic film comprising a plastic film, which is, if desired, at least on one side coated with ceramic material deposited using a vacuum thin layer deposition process, and a plastic layer deposited by extrusion coating on the plastic film or on the ceramic layer which may be present, such that the ceramic layer is situated between the plastic film and the plastic layer deposited by extrusion coating. Also within the scope of the invention is a process for manufacturing a composite film.
In composite plastic films comprising a substrate film and a plastic layer deposited by extrusion coating or laminate bonding the degree of bonding between the extruded layer and the substrate film is inadequate for many applications.
In order to improve the bonding between the substrate film and a plastic layer deposited by extrusion coating, it is known to employ modified copolymers and terpolymers of ethylene or propylene which often bond well.
The strength of the sealing seam is of decisive importance if a composite plastic film is to be used e.g. as a sealable film for packaging applications.
The object of the present invention is therefore to provide a composite plastic film of the kind described above in which the bond strength between the plastic layer deposited by extrusion coating and the substrate film is higher than in state of the art composite plastic films. A further objective of the invention is the provision of a suitable process for manufacturing such a composite plastic film.
That objective is achieved by way of the invention in which a metal layer of chromium, aluminum, nickel, titanium iron, molybdenum or an alloy made from at least two of these metals is provided as an aid to bonding between the plastic film, or ceramic layer which may be present, and the plastic layer deposited by extrusion coating. Preferred metals are chromium and aluminum, chromium being specially preferred. A preferred alloy is V2A steel.